The present invention relates to a video signal recording system which records reproduced normal video signals in a normal mode but prevents the normal recording of reproduced video signals provided with copy guards.
A current copy guard technique utilizes pseudo horizontal synchronizing pulses inserted in a portion of a vertical blanking interval. The pseudo pulses are equal to or higher than the black level, and more in number than normal. These pseudo pulses cause an auto gain control (AGC) circuit of a video signal recording system to vary the brightness of pictures. This copy guard system makes use of the difference in time constant between a television reproducing system and a video recording system.
This conventional copy guard system, however, tends to deteriorate the quality of recorded pictures because this system must increase the gain of the AGC circuit to some extent in order to improve the performance of the copy guard. Furthermore, these pseudo horizontal synchronizing signals occupy a considerable portion of the vertical blanking period, so that the use of the vertical blanking period for other data is limited.